This invention relates to electrophotographic copying apparatus capable of forming clear copies.
In electrophotographic copying apparatus of the type wherein a photosensitive sheet is mounted on the periphery of a rotary drum, an electrostatic latent image is formed on the surface of the photosensitive sheet and the latent image is developed with toner to form a toner image, the photosensitive sheet is sensitized by depositing electrostatic charge on the surface thereof, and a light image of an object is projected upon the sensitized photosensitive sheet through a slit while the drum is being rotated. Accordingly, when vibration or shock caused by the operation of the mechanisms of the copying machine other than the exposure device is transmitted to the exposure device or the rotary drum when it operates, the reproduced copy is not clear or is obscured. This phenomenon will be described in detail with reference to FIG. 1 of the accompanying drawing. In conventional electrophotographic copying apparatus, a charging device 1, an optical system 7, a developing device 2, a transfer printing device 3 and a cleaning device 4 are disposed so as to surround a rotary drum 5 provided with a photosensitive sheet, not shown. The optical system includes a suitable slit, not shown, and projects the light image of an original 6 onto the photosensitive sheet through the slit thus forming an electrostatic latent image, corresponding to the projected light image on the surface of the photosensitive sheet. The latent image is then developed into a visible toner image and the toner image is transfer printed onto a recording paper sent from a paper feeding device 8, in a manner well known in the art. In order to precisely transfer print the toner image onto the recording paper, it is necessary to advance beforehand the recording paper to a position immediately before the transfer printing device 3. Accordingly, the paper feeding device 8 should commence its operation when the exposure device operates. The conventional paper feeding device 8 is constructed to be actuated by a cam 9 mounted on the shaft of the rotary drum 5 for the purpose of reducing the size of the copying apparatus and for the purpose of operating the paper feeding device in synchronism with the rotation of the rotary drum 5. For this reason the rotary movement of a paper feed roller 10 which is rotated by an electric motor, not shown, is transmitted to the rotary drum 5 via a lever (shown by dot and dash lines in FIG. 1) and the cam 9 thereby causing the drum to vibrate.
Where the paper feeding device is provided with a cutter K as shown in FIG. 2 for severing a web of the recording paper paid out from a roll of the paper X for successively cutting the paper into a predetermined length, the vibration or shock generated by the operation of the cutter or paper feeding roller 10 is transmitted to the rotary drum 5 thereby producing obscure copies. Such shock or vibration is also produced by the operation of some of the other devices of the copying machine and is also transmitted to the exposure device, thus obscuring the reproduced image.
In the electrophotographic copying apparatus of the class described above it is also necessary to synchronize the operation of the paper feeding device with the rotation of the rotary drum in order to provide the recording paper at a predetermined area of the drum, that is, the image forming area of the photosensitive sheet.
To this end, there have been proposed a number of synchronous operating devices. According to one prior art device, a paper feeding roller is rotated continuously, and the roller is urged against the rotary drum in synchronism with the rotation thereof thus feeding the recording paper. According to another prior art device, the paper feed roller is normally held in contact with the recording paper and the rotation of the paper feed roller is started in synchronism with the rotation of the rotary drum. In each case, smooth feeding of the paper or accurate synchronism is difficult to obtain because the roller slips on the surface of the recording paper when the roller is started to rotate or brought into contact with the paper due to the resistance caused by the friction acting between adjacent sheets of the paper which are laminated. Furthermore, in a copying apparatus which is constructed such that the rotary drum is rotated one more revolution than the number of the recording papers, the rotation of the drum and the paper feeding operation are not always in synchronism.